SU748265A1 - Power factor measuring device - Google Patents

Description

The invention relates to electrical measuring equipment and can be used in the production of indicating devices and transducers for measuring power factor in three-phase power systems. An electromechanical phase meter is widely known for measuring the power factor by the Q / P ratio, where Q and P are reactive and the power of the three-phase system l is active. The disadvantage of this phase meter is the complex construction of the measuring mechanism, narrow frequency range, low resistance to mechanical and climatic impacts. - The closest in technical essence to the offer is a static device for measuring power factor, containing three-phase transducers of active and reactive power, balanced bridge and showing the device, the power factor of which is calculated after equilibrating the bridge with respect to the resistance of the shoulders of the bridge 2. . The disadvantage of this device is the indirect determination of the power factor, which requires a preliminary reading of the resistance values and the subsequent processing of the received data, i.e. the complexity of the measurement process. The purpose of the invention is to simplify the measurement process by obtaining a direct reading of the power factor on the instrument. It is achieved by the fact that in a device for measuring the power factor containing three-phase transducers of active and reactive power and showing a device, a three-phase reactive power transducer is made in the form of two pulse width modulators, each of which consists of a series-connected integrator, a comparison unit and a key amplitude modulators and adder, while the outputs of the keys are connected to the inputs of the respective integrators, the second inputs of the key are connected to the output of the three-phase reobrazovatel active power, comparing the second output unit is connected to the input of a respective amplitude modulator outputs am: mp | ggudnyh modulators soediyoyy inputs GyMviaTopa, to which output. the indicating device is connected, the second inputs of the integrators are connected to the input terminals of the voltage, and the second inputs of the amplitude modulators are connected to the input terminals of the current.

The drawing shows a block diagram of the device.

The device contains three-phase transducers 1 and 2 of active and reactive power and a indicating device 3. Reactive power transducer 2 contains two single-phase analogous elements, included by the Aron circuit software and built on the time-to-pulse conversion principle. Each single-phase converter element includes a pulse-width modulator consisting of an integrator 4, 5, a block 6, 7, and a key 8, 9 and an amplitude modulator 10, 11, an integrator 4, 5, block B, 7 key 8, 9 are connected in series. The outputs of the keys 8, 9 are connected to the inputs of the respective integrators 4, 5, the second inputs of the keys are connected to the output of the three-phase converter 1 of the active power, the second outputs are block. 6, 7 comparisons are connected from the input of the corresponding amplitude modulators 10, 11, the outputs of which are co. are connected to the inputs of the adder 12, to the output of which the indicating device 3 is connected. The second inputs of the integrators 4, 5 are connected to the input terminals of the voltage, and the second inputs of the amplitude modulators 10, 11 are connected to the input terminals of the current.

The device works as follows.

A stable reference voltage + Ep is supplied to the integrator input, which is complemented with an Input ng1WBV voltage. As a result, a linearly falling voltage arises at the integrator output, which decreases with a speed as long as the output voltage does not reach

 level triggered by the comparison circuit. The comparison circuit overturns and switches the reference voltage from H-EQ to. The output voltage of the integrator increases at a rate of up to a value. when the comparison circuit is switched to the initial state. In the scheme, periodic review of the xyllar process occurs, so the integrator and the comparison circuit are in the auto-oscillatory mode: with a natural frequency that is much higher than the frequency of the measured signals. The input signal of t and 3 n at saw oo brz and b gb yayyar and zhShmYM: r1gr 1Tbrg1 and, sledytl but, the moment of operation of the circuit

WHAT leads to a change in the duty cycle

748265

self-oscillation pulses, i.e. to obtain a width-modulated signal,

Durability is determined from the ratios:.

- (11: 1 ± -g (

5 g- EoUex where T +

, iTjj T - period of self-oscillations;

R, C - input resistance and capacitor of the integrator.

In this device, to measure 0 power factor as a reference level at the input of the integrator 4 ;, 5; An active power is supplied from the transducer 1 through the keys 8, 9, a signal proportional to the active power 5 P, while ensuring that the reference signal switches from + P to -P simultaneously with the trigger of block b, 7 of the comparison, the key is controlled by the width-modulated signal removed from the corresponding block b, 7 comparison. The latitude-modulated signal is applied to the amplitude modulator 10, 11, at the output of which the average value of the voltage will be proportional to the product

1. Wb2iI iL 5.

and.

BbVX., -R

where ,,,, -. ,, voltage and currents of the three-phase power system

reactive power of a single-phase converter element.

 A signal proportional to the total power factor of the three-phase power system is removed from the adder 12. The scale of the indicating device is graduated in terms of the power factor "

Claims (2)

1. Author's certificate of the USSR 193614, c. 01R 25/00, 01/03/6. 2.Hom to V.L. et al. Application of transducers for check phase meters. - Measuring equipment, 1977, No. 7, p.86. m ..